Just visit Amazon or some other store

Amish Country Popcorn | 6 lb Bag | Mushroom Popcorn Kernels | Old Fashioned with Recipe Guide (Mushroom - 6 lb Bag) https://smile.amazon.com/dp/B00M9NDB1Q/ref=cm_sw_r_cp_api_glt_fabc_BVD0QDNWBH4C7HVHAE8C

This is good but not perfectly shaped. More round than most, but, this is the best one

https://nuts.com/snacks/popcorn/mushroom.html

I've use this

And this

Both worked fine